Fatigue crack evolution and characteristic of cold recycled asphalt mixture in different dimensions

• Fatigue cracks evolution characteristic of CRME is studied by different dimensions. • The fatigue crack mainly propagates through the internal air void of CRME. • The fatigue cracks can be identified by vertical air void distribution of CRME. This paper aims at investigating the fatigue crack evolution and crack characteristics of cold recycled asphalt mixtures with asphalt emulsion (CRME) in different dimensional. Firstly, the fatigue resistance performance of specimens was studied by means of SCB fatigue test. A CMOS industrial camera was used to record the full process of SCB fatigue test. Then, X-ray CT technology was utilized to analyze the fatigue crack development rule and cracking behavior of CRME. Finally, SEM was used to investigate the microstructure and fatigue mechanism of CRME. The results indicate that the fatigue resistance of CRME is increased with the increase of curing time. The number of loading cycles when initial fatigue cracks appear in the surface of CRME during the fatigue test is recorded. More loading cycles when initial fatigue cracks appear, the longer the final fatigue life of the CRME is. Moreover, the fatigue crack mainly propagates through the internal air void in CRME, the increase of air void content under fatigue loading can reflect the fatigue damage to CRME. In addition, the cement hydration products and asphalt membrane formed by demulsification of emulsified asphalt are gradually combined to form a dense spatial structure to improve the fatigue cracking resistance of CRME during curing process. The research is meaningful to further understand the mechanism of fatigue cracking for cold recycled mixtures, and provide theoretical support for improving the fatigue cracking resistance.